BGP multihome Failover Question

bennordlander · ‎06-03-2002

I have DS3 to main provider

I am getting 2 T1s DIA to fail over to a different provider (don't want to use them unless i have to)

I am already set to bgp peer with DS3 provider, but will need to set up BGP peer with other provider shortly and set it up as failover. I want to advertise to both, but dont' want anything to do with load balance.

Q1) What is the optimal configuration for what i want to do?

here is my best guess for my scenario

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interface Hssi1

ip address y.y.y.y+1 255.255.255.252

interface serial2

ip adddress a.a.a.a 255.255.255.252

interface serial3

ip address b.b.b.b 255.255.255.252

BGP myASN

network x.x.x.x 255.255.192.0

neighbor y.y.y.yremote-as DS3provider_ASN

neighbor y.y.y.y filter-list 10 out

neighbor y.y.y.y soft-reconfiguration inbound

neighbor y.y.y.y route-map ABC out

neighbor z.z.z.z remote-as 2T1provider_ASN

neighbor z.z.z.z filter-list 10 out

neighbor z.z.z.z soft-reconfiguration inbound

neighbor z.z.z.z route-map ABC out

no auto summary

ip as-path access-list 10 permit ^$

route-map ABC permit 10

match as-path 10

ip route 0.0.0.0 0.0.0.0 y.y.y.y 5

ip route 0.0.0.0 0.0.0.0 z.z.z.z 10

ip route z.z.z.z 255.255.255.252 a.a.a.a

ip route z.z.z.z 255.255.255.252 b.b.b.b

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Q2) If this works right.. how does the incoming traffic come in as far as choosing where to come in through. They are just going to use whatever is closer/faster? Any way to control that?

Thanx in advance

Faraz Shamim · ‎06-04-2002

Hello Ben,

Your configuration will not work. Here is the correct configuraiton:

router bgp

network x.x.x.x 255.255.192.0

neighbor y.y.y.y remotge-as DS3provider_ASN

neighbor y.y.y.y weighth 200 <------This will always prefer this link for all outgoing traffic

neighbor y.y.y.y filter-list 10 out

neighbor y.y.y.y soft-reconfiguration inbound

neighbor z.z.z.z remote-as 2T1provider_ASN

neighbor z.z.z.z filter-list 10 out

neighbor z.z.z.z soft-reconfiguration inbound

!! The following configs below will help in advertising your network with worst path to the outside world. Now there is always a possibility that the outside world may have their outgoing policy that will override this but this configs work in most cases !!

neighbor z.z.z.z route-map asprepend out

ip as-path access-list 10 permit ^$

route-map asprepend

match as-path 10

set as-path prepend

Hope it help,

Faraz